Active-safety subsystems of a vehicle are defined as subsystems that have the capability to monitor the state of the vehicle or detect and/or communicate with stationary or mobile objects external to the vehicle in order to assist in maintaining the safety of the vehicle, its occupants, other humans and the environment in which the vehicle and occupants are travelling.

In automotive engineering the functions/subsystems that have the potential to prevent harm to people and property include, amongst others - adaptive cruise control (ACC), electronic stability control (ESC), collision avoidance, collision damage mitigation, lane and road departure control, and overtaking control. Underlying and effectuating the intent of these functions is the entire real-time control system of the vehicle – drivetrain, braking, steering and active suspension. Overlying the active safety systems should be a safety supervisory system that resolves intelligently the natural conflicts and ambiguities that arise when multiple active safety subsystems, being concurrently active, react in real time to circumstances that trigger their intended response.

For road and traffic authorities, the functions/subsystems that currently cause harm to the environment and simultaneously have the potential to mitigate these effects include, the drivetrain which consumes air and fuels and produces gaseous and particulate emissions, and the braking and steering systems which produce particulate emissions.